Body mass index reference norm for screening overweight and obesity in Chinese children and adolescents

Abstract

Objective To establish a national body mass index (BMI) reference norm for the purpose of screening and more active prevention and cure on overwight and obesity in Chinese children and adolescente. Methods The 2000 Chinese National Survey on Students Constitution and Health was used as reference population. In total there were more than 244.2 thousands of primary and secondary Han nationality students aged 7 through 18 years old included in this study. The BMI distribution of various Chinese children and adolescent groups were compared with the NCHS international norm, the percentage values and with advanced ages, were calculated. In the beginning, three temporary norms were set up, using the different combination of P85, P90 and P95 BMI percentages. Based on the intersect testing and varifying of physiological, lipidemia biochemical and body composition measures, the best norm was then selected. B-spline smoothing method was used to correct the curves, both for males and females, composed by cut-off points at different ages. Results Using samples from the costal developed metropolis, the BMI curves successfully overcame the shortcomings of low and depressive phenomenon of the total population, in particular after the mid--adolescent period. The temporary Norm Ⅱ, composed by cut-off points of P85 for overweight and P95 for obesity, was found to be the best among the three temporary norms, both shown by its sensitivity and specificity. 24 and 28 were used as cut-off points for overweight and obesity in this norm, both for males and females aged 18 years. These two cut-off points were consistent with those shown in the Body Mass Index Reference Norm for Screening Overweight and Obesity in Chinese Adults. Three Samples from Beijing, Henan and Sichuan, used as representatives of upper, middle and relative low levels of physical growth of children and adolescents in China, were used for extra tests. The screening results showed that among the male and female subjects aged 7 through 18 years, the prevalence rates were 17. 00% and 9. 46% for overweight, 9. 99% and 6. 47% for obesity in Beijing while 10. 86% and 6. 64% for overweight, 4.27% and 3.07% for obesity in Henan, and 6.95% and 4.23% for overweight and 2. 84 % and 2. 09 % for obesity in Sichuan, respectively. Data clearly showed that the results were in accordance with the actural situation seen in the Chinese studens in 2000. Conclusion The newly established reference norm seemed to be good for prospective studies as it considered the facts regarding the rapid and strong tendency of secular growth changes seen in the Chinese children and adolesconts. It also decreased the difference of growth levels between the Chinese children and adolescents and those of the international norms. Ths norm was particularly developed for the Chinese which was also in consistent with the Eastern Asia ethnic charcteristics so could be promoted in China.